Avian prey intake and breeding success parity of the powerful owl in dry, inland Victoria

Abstract

Apex predators are vulnerable to environmental changes which can cascade through trophic levels of an ecosystem. Investigating prey-predator relationships is important for directing conservation efforts and understanding how species may respond to ecosystem changes. This case study examined the diet and breeding success of the threatened powerful owl Ninox strenua in central Victoria where the box-ironbark forests have undergone widespread clearing, fragmentation, and degradation. The powerful owl preys predominantly on arboreal mammals, however, some birds are also consumed. By analysing the contents of regurgitated owl pellets of two owl pairs, we found that birds comprised 29.3% of all prey items and contributed the largest proportion of prey biomass for one pair (34.4%). All mammalian prey species identified in the pellet remains are dependent on tree hollows, which are now a scarce and competitive resource in box-ironbark forests. Despite consuming a diet lower in mammalian prey than found in other studies, breeding success over five consecutive years was 1.4 chicks fledged per pair per year, which is notably higher than historical observations in the region and similar to powerful owls in other parts of their distribution. Our observations suggest that flexibility in prey selection enables powerful owls to occupy ranges that have undergone significant ecosystem change.